RESUMEN

This study was designed to determine the effects of four well-characterized dietary brans on large bowel tumorigenesis induced in mice with 1,2-dimethylhydrazine (DMH). Eight-week-old barrier-derived male Balb/c mice were fed a semisynthetic diet with 20% bran added (either corn, soybean, soft winter wheat, or hard spring wheat) or a no-fiber-added control diet. Half of each group was given DMH (20 mg/kg body weight/week, subcutaneously for 10 weeks) beginning at 11 weeks of age. Surviving mice were killed 40 weeks after the first DMH injection. Tumors were not found in mice not subjected to DMH. In DMH-treated mice, tumors were found almost exclusively in the distal colon. Tumor incidences were as follows: controls, 11%; soybean group, 44%; soft winter wheat group, 48%; hard spring wheat group, 58%; and corn group, 72%. Tumors per tumor-bearing mouse ranged from 1.4 to 1.6, except in the corn group, which had 2.1. A positive correlation was found between percentage of neutral detergent fiber in the brans and tumor incidences but not between the individual components of cellulose, hemicellulose, or lignin. The enhancement of DMH-induced large bowel tumorigenesis by all four bran types may reflect a species and/or mouse strain effect that is bran-source related. These data emphasize the importance of using well-defined bran in all "fiber" studies.

Asunto(s)

RESUMEN

Bean golden mosaic virus (BGMV) contains predominantly circular single-stranded DNA, but DNA isolation by treating virus with proteinase K results in conversion of the DNA to a linear form. The conversion is inhibited by as little as 0.025% sodium dodecyl sulfate but not by phenylmethylsulfonyl fluoride and does not occur when purified DNA is incubated with proteinase K. Protein is not involved in the covalent structure of BGMV DNA; the conversion appears to be caused by an endonuclease that copurifies with the virus and is resistant to proteinase K. BGMV contains a major capsid protein with an estimated molecular weight of 27,400. Two minor proteins are found, even in the most highly purified virus preparations; their origin and role in virus structure or function are unknown. BGMV particles contain 19% DNA; therefore each geminate particle must contain a single DNA molecule, of which over 90% are circular. The estimated molecular weight of the virus is 3.8 x 10(6).

Asunto(s)

RESUMEN

The involvement of the free space in phloem loading of sucrose was studied in sugar beet source leaves (Beta vulgaris, L.). Sucrose, supplied exogenously to the abraded upper surface of leaves at a concentration of 20 mm, was available for translocation at rates similar to those obtained with photosynthesis. The exogenous sucrose substituted as a source of translocate for assimilate derived from photosynthesis when the latter process was disrupted by plasmolysis of the leaf with 0.8 M mannitol. The mesophyll symplast was not completely disrupted by this treatment, however. Data from the sugar uptake experiments indicate that phloem loading can occur from the free space.Isotope trapping of labeled sugars derived from (14)CO(2) was used to intercept and identify sugars passing through the free space prior to phloem loading. Increased translocation rates induced by 4 mm ATP or increased light intensity were accompanied by increased trapping of sucrose but not of glucose. The data support the view that sucrose passes into the free space prior to phloem loading.